Speaker
Description
Summary
The distribution of power in future LHC experiments represents a difficult
engineering challenge, given the global requirements in terms of power needs,
available cooling capacity and limited material budget. The harsh radiation
environment (up to several Mrd in Total ionizing Dose) requires all the electronics
to be radiation tolerant and the intense magnetic field (up to 4T) makes conventional
switching converters unusable in many locations.
In view of LHC upgrades where front-end circuits might require even larger supply
currents, it is necessary to evaluate an alternative power distribution scheme. This
could be based on the distribution of higher voltage (24 -48V) from external power
supplies to converters installed locally inside the detectors that have to convert
the power to the low voltage and high current required by the front-end circuits. Due
to the vicinity of the switching converter to the sensitive detector elements, EM
noise has to be carefully studied.
We are evaluating a solution involving an inductor based switching DC-DC step-down
converter. A preliminary analysis is in progress in order to understand the
feasibility and availability of the different components of the converter that match
the above requirements.
We have selected a 0.35 um CMOS technology usually employed in automotive
applications. This technology can stand up to 80V and it can be made radiation
tolerant with some modification to the layout. Irradiation results on leakage current
and threshold voltage shift up to 80 Mrad will be shown.
As regular ferromagnetic inductor cores saturate in such high magnetic field we are
evaluating different air core inductor designs. To avoid EM noise we studied the
emitted magnetic field from differently shaped air core inductors (solenoidal and
toroidal). Inductors of 500nH made by 32 turns with a volume of 340mm^3 were
simulated with a 3D finite element program with a current of 1A. The results
illustrating the residual magnetic field for different geometries will be shown.
A simulation program was written to evaluate the efficiency of this converter, taking
into account the parameters and parasitic values of the CMOS technology, inductor and
capacitor and using different values of input voltage, output current and voltage. We
will show that an efficiency above 80% could be achieved. In the nominal case of
input voltage equal to 24V, output voltage 2.5V, output current 1A, switches
on-resistance 110mOhm, inductance 500nH and at a frequency of 1Mhz, the efficiency is
89%.
